McKinney J.D., Warnick C.C. Microhydropower Handbook Volume 1
Подождите немного. Документ загружается.
4.1.5 Regulating Turbine Speed
*
electric power qenerated by a
With only a few exceptions, the
hydropower installation must be regu
second (Hz) to be useful in powering
lated to a frequency of 60 cycles per
motors and appliances.
Notable
exceptions would be using a turbine for producing mechanical power to drive
equipment directly, and electric generation for the purpose of space or
water heating,
or absorption refrigeration.
Maintaining constant electric power frequency and voltage requires
that the turbine be operated at constant speed.
In commercial hydropower
installations, turbine speed control is Ferformed by a governor that senses
generator frequency and positions the turbine nozzle spear valve, wicket
gates, or runner blade angle to maintain 60-Hz power. These methods of
speed control are designed to maintain a high turbine efficiency over a
wide range of flows and corresponding power output.
The cost of
conventional governor mechanisms may well be prohibitive for
microhydropower installations.
i
' . .
It is possible to operate a microhydropower installation
interconnected to a power utility without benefit of a speed governor.
Such installations are manually brought on line, and once set, they will
supply to the utility the amount of power that corresponds tc the hydra
energy supplied to the turbine.
Speed control of such an installation is
inherently maintained, for normal operating limits, by the natural
characteristics of the system after it is connected to the power utility.
The operation can continue indefinitely, provided that variations in water
flow and head stay within reasonable limits. In effect, the power utility
is providing speed control for this mode of operation.
If the power plant is to be operated without a connection to a pcwer
utility, as in a Category 1 installation, then some form of speed
regulation is probably a necessity.
A less costly method of speed regulation for sma
1 turbines and pumps
used as turbines is to use an electronic load control
device.
Electronic
4.1-17
_. :
_.
load control allows stand-alone generation of regulated 60-Hz power. These
devices sense the power frequency and adjust a variable fraction of the
electric load to maintain the turbine-generator speed constant at 60 Hz.
The range of power output that is varied to maintain constant turbine speed
depends on the amount of water power that is available, and the variations
in electric load demanded from the unit.
These factors must be defined and
analyzed by a supplier of electronic regulation units to determine if this
method is feasible and economic for your installation.
The power
dissipated by the controller to maintain constant speed can be put to use
for space or water heating,
absorption type refrigeration, or rejected as
heat by resistors placed in the turbine water flow stream.
These methods are explained in more detail in Subsection 4.8.
The conventional speed regulator discussed at the beginning of this
subsection is a mechanical governor that controls inlet water-flow to the
turbine.
A relatively recent development is the use of electronic speed
sensors and microprocessors to control inlet water flow. This type of
speed regulation should be more economical than the conventional governor
system but may be difficult to purchase from conventional equipment
suppliers.
Some microhydropower developers have been very successful using
innovative methods of speed contrel-.
4.1.6 Turbine Setting
The setting of a reaction turbine in relation to the minimum tailwater
elevation can have a significant impact on the life of the turbine.
Improper turbine setting can lead to the phenomenon known as cavitation,
which results in pitting of the runner.
In reaction turbines, reduced
pressures occur in the hydraulic passages as the fluid is accelerated to
high velocities,
and vapor bubbles form in the flowing stream.
When these
bubbles are then carried into a region of higher pressure, they can
collapse rapidly. If this collapse occurs adjacent to the runner surface,
it results in the removal of a small amount of the metal, and this process,
if allowed to continue, accelerates with time.
Thus, the cavitation that .
causes this type of damage to a turbine is to be avoided.
4.1-18
Excessive cavitation damage can be avoided by setting the horizcntal
centerline of the turbine's runner a specified distance above or below the
tailwater elevation.
The correct distance should be supplied by the
turbine manufacturer and should be closely adhered to. From an equipment
standpoint, a deep setting is better because it provides sufficient
pressure at the runner discharge to allow the use of smaller, higher speed
turbines, and therefore lower cost units, without excessive cavitation.
The civil costs will be greater with the deeper setting because of
additional excavation and more powerhouse work. A balance should be
maintained between the civil costs and the equipment costs as determined by
the turbine setting. For a further discussion on turbine setting, see
Appendix A-7.
The setting of impulse turbines in relation to the tailwater elevation
is not critical for prevention of cavitation. Impulse turbines are
generally located as close as possible to the tailwater elevation to use as
much of the available head as is possible, but they must run free of any
tailwater interference.
4.1.7 Draft Tube
This section discusses draft tubes for reaction turbines. If you have
an impulse turbine, the contents of this section are not important to you.
Reaction turbines (Francis, propeller, and pumps-as-turbines) operate with
the flow path completely filled with water. This allows the turbine to be
mounted above the tailwater, and still use the full available head by means
of a draft tube. A draft tube is a conical pipe, straight or curved
depending on the turbine installation,
that maintains a column of water
between the turbine outlet and the downstream water level. Water leaves
the turbine runner at a relatively high velocity, constituting a
substantial portion of the total energy available. To recover this energy
efficiently, the velocity must be reduced gradually and friction losses
minimized. If the velocity is not reduced, the water will spill out the
end of the turbine outlet into the tailwater, and the energy contained in
the flowing water will be dissipated as turbulence in the tailrace.
4.1-19
L..
The draft tube outlet must remain below the water surface at all water
levels to prevent air from entering the tube and displacing the water
column.
It is the velocity of the water in the draft tube that acts, when
This suction head can be
reduced, as a suction head on the turbine runner.
enhanced by converting part of the flow velocity to pressure within thge
draft tube.
This requires a tube of expanding flow area, with the diameter
at the tube outlet about two times
the diameter at the inlet, where it
attaches to the turbine.
The angle between the opposite walls of the
expanding draft tube should be between 7 and 20 degrees to give optimum
pressure recovery.
The design of the draft tube for a,commercially
manufactured turbine should be approved by the manufacturer.
The majority of microhydropower sites will use straight conical draft
tubes, (see Figures 4.1-Z and 4.6-4).
For preliminary layout purposes, the
draft tube outlet diameter should be twice the turbine runner diameter and
the length of the tube should be four times the runner diameter. The *
bottom of a vertical conical draft tube should not be closer than one
runner diameter to the bottom of the tailrace.
The tailrace width for a
vertical conical draft tube should be four turbine runner diameters, but
can be only two diameters wide for a horizontal draft tube.
There are other draft tube designs that use curved sections to reduce
the amount of excavation required.
These are elbow or "S" shaped and -
should be designed by the turbine manufacturer on the basis of his model
tests.
4.1-20
4.2 Contact Turbine-Generator Manufacturers and Suppliers
Microhydropower developers will want to select a standard turbine and
not undergo the expense of having a turbine specifically designed to meet
the site characteristics.
To select a standard turbine-generator unit that
will generate the most energy for the dollar, you should contact various
suppliers and request them to recommend the unit that they feel best fits
your site.
Use the form that follows to provide the information the manu-
facturer will need.
Provide as much information as possible to aid the
manufacturers and suppliers in determjning which unit to recommend. Pic-
tures and drawings should be included if available.
Identical information
should be supplied to all manufacturers and suppliers so that you can eval-
uate the responses fairly. A listing of manufacturers and suppliers is
included as Appendix F, and additional forms can be found in Appendix I.
To aid your understanding of the form, a narrative description
rePerring to the major headings of the form is provided below.
I.
REASON FOR DEVELOPMFNT
.
By choosing the most appropriate category, you are telling
the manufacturer or supplier why you desire to produce power. If
you state that you want to be able to generate power independent
of the utility, you will be able to generate power when the util-
ity service is interrupted or even if disconnected from the util-
ity.
This tells the manufacturer or supplier that he must supply
a more expensive synchronous generator, along with speed regulat-
ing equipment.
(G
enarators are discussed in Subsection 4.8). If
you state that you don't mind being dependent on the utility,
then the recommended generator will probably be an induction gen-
erator, which will use a less expensive motor starter for
switchgear.
4.2-l
---- . .
II. TYPE OF SOURCE AND AMOUNT OF HEAD
Choose the category that best describes your type of source
,(Subsection 2.6), and give the available head (Subsection 3.4).
If you are a run-of-the-stream developer and you have a fixed
head, list that head. If you are not sure you have selected the
best head, list the ranges of head available so that the manufac-
turer or supplier can select the head that best fits his
equipment.
If the site is an existing dam which has a fluctuating head
(Subsection 3.5.4), describe the characteristics of the fluctua-
tion.
In the additional comments, include an explanation of how
the head fluctuation corresponds to flow variations.
III. AMOUNT OF FLOW
If you have deve
include a copy of the
loped a flow durat
curve. This will
ion curve, be sure and
help the manufacturer or
supplier to optimize his turbine selection.
If you have estimated
*flow on the basis of an average monthly flow value, then include
that information.
If you have a source,
such as a canal, that
flows only during part of the year, be sure and include that
information.
IV. PERSONAL POWER NEEDS
List the results you obtained from Subsection 3.1.
v.
ADDITIONAL INFORMATION
Include any additional information that might aid the manu-
facturer or supplier to evaluate your site requirements. Call
the utility to learn how far the nearest substation is from your
Site.
This distance will determine whether or not an induction
generator can be used.
4.2-2
If you are developing an existing site with a turbine already
installed and you would like to consider using it again, write
the original turbine manufacturer to obtain information. In
addition to the site data included above, send the following
information, if available:
Name of the site
Name of the original turbine.purchaser
Date the turbine was purchased
Contract number
Name plate data
Drawing numbers of the turbine.
After receiving the responses back from the manufacturer or
supplier, proceed to the next section to make a preliminary cost
estimate, decide whether or not to proceed, and establish design
criteria.
4.2-3
.
-_ - _-._._ - __... -.-.--._-... ___~ .-._.....-. -
_
MICROHYDROPOWER TURBINE GENERATOR
INFORMATION REQUEST
(DATE)
GENTLEMEN: *
I am interested in installing a microhydropower system. The following
site specifications are supplied for your evaluation.
Please review the
specifications and answer any appropriate questions concerning your
equipment.
My Name:
Phone No. (
)
Project Name:
Address: _
-
I.
REASON FOR DEVELOPMENT
(Check One)
1
- :
- 2.
3.
- 4.
5.
I am interested in supplying my‘own electrical needs. I do not
plan to intertie wi,th a utility. Therefore, I will require a
synchronous generator.
I am interested in supplying my own electrical needs, When my
needs are less than the energy produced, I would consider selling
to a utility. However, I want to be able to generate power
independent of a uti1.L~.
I therefore require a synchronous
generator and speed control equipment.
I am interested in supplying my own electrical needs. I want to
be able to sell excess power to a utility. An induction generator
is acceptable since I do not care to generate power independent
of the utility.
I am interested in generating as much power as possible for the
dollar invested.
However, I want a synchronous qenerati_sr so that
I can generate power if the utility service is interrupted.
I am interested in generating as much electrical power as possi-
ble for the dollar invested.
I am not interested in generating
independent of the utility.
4.2-4
,
I
I
i
L.- ’
II. TYPE OF SOURCE AND AMOUNT OF HEAD
(Check One)
1.
The site is a run-of-the-stream site and can have a pool-to-pool
head from to
feet.
- 2.
The site is an existing dam and has a constant/variable pool-to-
pool head of
to
feet.
3.
The site is a canal drop/industrial waste discharge and has a
pool-to-pool head of
feet.
III. AMOUNT OF FLOW
(Check One)
1.
The flow values are based on the attached flow duration curve.
- 2.
The flow value is based on a minimum stream flow of
cfs.
This is because my objective is to supply my energy
needs as much of the year as I can.
3.
The flow is available
constant at
cfs.
4.
The flow values are based on
months out of the year and is fairly
monthly averages in cfs:
Jan.
May
Sept.
Feb. Jun.
Oct.
Mar. Jul.
Nov.
Apr. Aug.
Dec.
5.
Other: See V-9, Additional Information.
IV. PERSONAL POWER NEEDS
A copy of the daily load use table is attached. The daily peak load
is estimated to be
kW. Major electrical equipment is listed
below.
The voltage I need is
9
and is single/three phase.
4.2-5
!
I
-.---. - _. _
.._ __ ._ _ _
.-_-~- - _._ _.
.,_
.-.__ . . .-. -._- ._...-.__.
_ --._..
V.
ADDITIONAL INFORMATION
i
1.
Site location and stream name
2.
Name of local utility
Distance to nearest substation is miles,
3.
The quality of the water is usually clear/murky/silt laden/muddy.
4. Site elevation is
feet.
5.
Annual average temperature variation is from
to
OF.
r
0.
A sketch of the site is/is not included.
7.
Existing structures or equipment that should be used, if
possible, include
. 8.
The proposed diameter and length of the penstock are (leave blank
if not known): inches in diameter,
feet in
length.
9.
Additional information to be considered
4.2-6
I
t